Recently, various types of electronic equipment, such as a cellular phone and an electronic camera, have advanced in functions and are becoming diversified. Moreover, such equipment mounted with a light transparent touch panel on a display surface of their display devices, such as liquid crystal display devices, are increasing in number.
Such equipment have been increasing that a user can press the touch panel with a finger or a pen while viewing display on the rear display device through the touch panel in order to make a transfer among their various functions and also those equipment are desired to be easy to see and operate.
Such a conventional touch panel will be described with reference to FIGS. 5 and 6. It is to be noted that the drawings are shown in a partially enlarged size so that a configuration can be understood easily.
FIG. 5 is a cross-sectional view of conventional touch panel 140. FIG. 6 is an exploded perspective view of conventional touch panel 140. In FIGS. 5 and 6, conventional touch panel 140 includes film-shaped light transparent upper substrate 101, light transparent lower substrate 102 made of glass or the like, light transparent upper conductive layer 103 made of indium tin oxide formed on a lower surface of upper substrate 101, and lower conductive layer 104 formed on an upper surface of lower substrate 102.
To ends of upper conductive layer 103 in direction 150A, a pair of upper electrodes 105A and 105B are connected, respectively. To ends of lower conductive layer 104 in direction 150B perpendicular to direction 150A, a pair of lower electrodes 106A and 106B are connected, respectively. Upper electrodes 105A and 105B and lower electrodes 106A and 106B are made of a conductive material, such as silver. Upper electrodes 105A and 105B and lower electrodes 106A and 106B extend to connection portions 101A and 102A at peripheral left ends of upper substrate 101 and lower substrate 102, respectively.
On the upper surface of lower conductive layer 104, a plurality of dot spacers made of an insulating resin are formed with predetermined spacing between the dot spacers. A peripheral inner fringe between upper substrate 101 and lower substrate 102 is fitted with roughly frame-shaped spacer 107.
The respective peripheries of upper substrate 101 and lower substrate 102 are adhered to each other with an adhesive agent applied to both or one of the upper and lower surfaces of spacer 107 so that upper conductive layer 103 and lower conductive layer 104 may face each other with a predetermined interval provided between them.
A plurality of wiring patterns 109 are formed on at least one of upper and lower surfaces of film-shaped wiring board 108. Film-shaped cover sheet 110 is adhered to the lower surface of wiring board 108, to cover the plurality of wiring patterns 109 except right and left ends of wiring patterns 109.
A right end of wiring board 108 is held in a condition where it is sandwiched by respective left-end connection portions 101A and 102A of upper substrate 101 and lower substrate 102. A right end of each of wiring patterns 109 is adhered and connected to upper electrodes 105A and 105B and lower electrodes 106A and 106B with a conducting adhesive agent. The conducting adhesive agent may include an anisotropic conducting adhesive agent in which conducting particles are dispersed in a synthetic resin.
Film-shaped display sheet 111 has light transmitting portion 111A, light shielding portion 111B, and operation portion 111C. Light transmitting portion 111A is formed at the middle on a lower surface of display sheet 111. Light transmitting portion 111A is surrounded by light shielding portion 111B painted in a predetermined color and operation portion 111C on which patterns such as characters and symbols are printed. Adhesion layer 112 formed all over the lower surface of display sheet 111 causes display sheet 111 to be adhered to the upper surface of upper substrate 101.
Touch panel 140 having such a configuration is disposed on the display surface of the display device such as a liquid crystal display device and mounted on the electronic equipment. The left ends of the plurality of wiring patterns 109 on wiring board 108 are electrically connected to an electronic circuit of the equipment by using a connector or soldering.
If the upper surface of light transmitting portion 111A or the upper surface of operation portion 111C on display sheet 111 is pressed with a finger or a pen in response to display on the display device disposed on the lower surface of lower substrate 102 of touch panel 140, upper substrate 101 below display sheet 111 bends. The pressed position on upper conductive layer 103 comes in contact with lower conductive layer 104. A voltage is sequentially applied to the pair of upper electrodes 105A and 105B and the pair of lower electrodes 106A and 106B through the plurality of wiring patterns 109 on wiring board 108 from the electronic circuit. The pressed position is detected by the electronic circuit based on a ratio between a difference in potential across upper conductive layer 103 and a difference in potential across lower conductive layer 104, thereby switching various functions of the equipment.
In condition where a plurality of menus, for example, are displayed on the display device disposed on the lower surface of lower substrate 102 of touch panel 140, an operator presses light transmitting portion 111A or operation portion 111C on a desired option of the menus. The operated position is detected by the electronic circuit via the plurality of wiring patterns 109 on wiring board 108. The operator can select and decide on the desired one of the plurality of menus.
FIGS. 7A and 7B are cross-sectional views of conventional touch panel 140.
In such conventional touch panel 140, irregularities occur in such a manner as to cause a wave portion at a left end of display sheet 111 as shown in FIGS. 7A and 7B. Accordingly, there are some cases where display on the display device of touch panel 140 cannot be seen clearly through light transmitting portion 111A.
A touch panel similar to touch panel 140 is disclosed in Unexamined Japanese Patent Publication No. 2009-277121.